A fuel tank ventilation device is typically located between a fuel tank and the atmosphere outside the tank, to prevent overpressure conditions within the tank. For example, FIG. 1 shows a ventilation device 20 of a fuel tank 10 according to the prior art. As shown, the ventilation device 20 includes a single pressure relief valve mounted to an upper wall 11 of the tank 10. But such ventilation devices are rarely in direct contact with the upper wall 11 of the tank 10, and are often placed at some distance from the tank 10 inline within a ventilation conduit, which is in fluid communication with the interior of the tank 10. And, in some fuel tank configurations, a ventilation device may be located within a common ventilation conduit, which is in fluid communication downstream of several ventilation conduits, which are individually in fluid communication with a fuel tank.
Ventilation devices often take the form of a pressure relief valve or a vapor recovery canister. Pressure relief valves allow gases within a fuel tank to escape to the atmosphere outside the tank to prevent a build up of pressure within the tank, and some pressure relief valves also allow gases from the atmosphere to enter the interior of the tank so as to prevent a vacuum condition or under pressurization within the tank. Vapor recovery canisters typically contain an activated carbon element, which captures gases escaping from the tank when there is a build up of pressure therein and thereby prevents such gases from escaping into the atmosphere. When pressure in the tank drops below the pressure in the vapor recovery canister, the captured gases flow back into the fuel tank.
Unfortunately, however, when the ventilation device opens to allow gases within the tank to exit the tank, liquid contained in the tank may also escape and may damage a pressure relief valve, particularly when the liquid is a fuel additive diluted in solvent. In such a case, when the liquid fuel additive comes into direct contact with the pressure relief valve and is exposed to air, the solvent eventually evaporates, thereby leaving only fuel additive. The additive tends to solidify around various parts of the pressure relief valve, thereby rendering the valve ineffective for its intended purpose. For example, valve seals may dry out and bond to other parts of the valve.
Another problem occurs where the ventilation device is a vapor recovery canister, wherein liquid fuel may flow out of the fuel tank and into the vapor recovery canister. Activated carbon within the canister can thus become impregnated and contaminated with liquid fuel, thereby rendering the vapor recovery canister ineffective for its intended purpose.